This invention relates generally to image-forming machines with densitometers. More particularly, this invention relates to diagnostic systems for densitometers used in electrophotographic image-forming machines.
Image-forming machines are used to transfer images onto paper or other medium. Generally, a photoconductor is selectively charged and optically exposed to form an electrostatic latent image on the surface. Toner is deposited onto the photoconductor surface. The toner is charged, thus adhering to the photoconductor surface in areas corresponding to the electrostatic latent image. The toner image is transferred to the paper or other medium. The paper is heated for the toner to fuse to the paper. The photoconductor is then refreshedxe2x80x94cleaned to remove any residual toner and chargexe2x80x94to make it ready for another image.
Many image-forming machines use a densitometer to assist operating and controlling the image-forming process. The densitometer has an emitter and a collector on opposite sides of the photoconductor. In a transmission densitometer, the optical path passes from the emitter through the photoconductor to the collector. The densitometer provides a voltage reading corresponding to the amount of light energy passing from the emitter to the collector. The voltage reading also corresponds to the density of the photoconductor and any toner on it. By comparing a voltage reading of the photoconductor to a voltage reading of the photoconductor with toner, a net voltage reading may be obtained that is indicative of the toner on the photoconductor. The densitometer typically works with a process patch, which is on the surface of the photoconductor in an interframe or edge area. As the image-forming machine operates, the process patch is charged, exposed, and developed to provide the maximum toner density on the process patch. The densitometer determines the optical density of toner on the process patch, from which operating adjustments are made.
Generally, an optical filter is used to determine the performance of the densitometer. A portion of the photoconductor, without toner, is positioned in the optical path of the densitometer. A voltage reading of the photoconductor is taken. The optical filter is attached to a wand and projected into the image-forming machine so the optical filter blocks the optical path of the densitometer. The optical filter reduces a predetermined amount of light energy passing through the photoconductor to the collector. A voltage reading of the photoconductor with the filter is compared to the voltage reading of the photoconductor without the filter. If the difference in the voltage readings is within a particular range for the filter, the densitometer is deemed to be operating within specifications.
The optical filter is difficult to use and provides subjective voltage readings. When projecting the filter and wand into the image-forming machine, care must be taken not to damage other parts and not to scratch or mark the filter and the photoconductor. Additionally, care must be taken to position the optical filter properly in front of the emitter. The filter may be held at an angle in relation to the emitter. The filter may be held too close or too far from the emitter. The filter may be moved while the voltage reading is taken. There may be additional variability from the experience level of the person performing the diagnostic procedure. In addition, the optical filter and wand are rather awkward pieces of equipment to carry. The filter also must be protected from damage when not in use.
Accordingly, there is a need for densitometer diagnostic systems in image-forming machines that have greater reliability and ease of use.
This invention provides a diagnostic system for a densitometer in an image-forming machine. The densitometer diagnostic system has diagnostic circuitry that reduces the drive current to the emitter in the densitometer by a known or calculable value. The output voltage from the amplifier circuitry in the densitometer is reduced in proportion to the reduction in the drive current. The densitometer output voltage with the diagnostic circuitry is compared to the densitometer output voltage without the diagnostic circuitry. The difference in the output voltages is compared to an output voltage specification associated with the diagnostic circuitry. When the difference in the output voltages essentially matches or is essentially within the range of the output voltage specification, the densitometer is functioning within specifications.
An image-forming machine with a densitometer diagnostic system may have a photoconductor, one or more chargers, an exposure machine, a toning station, and a densitometer. The chargers, exposure machine, and toning station, are positioned adjacent to the photoconductor. The charger or chargers electrostatically charges the photoconductor. The exposure machine optically exposes and forms an electrostatic image on the photoconductor. The toning station applies apply toner on the photoconductor. The toner has a charge to adhere to the electrostatic image.
The densitometer may have an emitter, a collector, amplifier circuitry, and diagnostic circuitry. The emitter and a collector are positioned adjacent to the photoconductor. The collector collects emissions from the emitter. The amplifier circuitry provides a voltage supply to the emitter and receives a current signal from the collector. The amplifier circuitry provides at least one output voltage based on the current signal. The diagnostic circuitry is connected to the amplifier circuitry and the emitter. The diagnostic circuitry reduces the drive current to the emitter.
A densitometer diagnostic system for an image-forming machine may have an emitter, a collector, amplifier circuitry, and diagnostic circuitry. The collector is positioned to collect emissions from the emitter. The amplifier circuitry provides a voltage supply to the emitter and receives a current signal from the collector. The amplifier circuit provides an output voltage based on the current signal. The diagnostic circuitry is connected to the amplifier circuitry and the emitter. The diagnostic circuitry reduces the drive current to the emitter.
In a method for diagnostic testing of a densitometer in an image-forming machine having a photoconductor, a first output voltage is obtained from the densitometer for the photoconductor. The diagnostic circuitry is connected to the densitometer. A second output voltage is obtained from the densitometer for the photoconductor. An output voltage difference from the first and second output voltages is determined. The output voltage difference is compared to an output voltage specification.
In an alternate method for diagnostic testing of a densitometer in an image-forming machine having a photoconductor, the diagnostic circuitry is connected to the densitometer. A first output voltage is obtained from the densitometer for the photoconductor. The diagnostic circuitry is disconnected from the densitometer. A second output voltage is obtained from the densitometer for the photoconductor. An output voltage difference is determined from the first and second output voltages. The output voltage difference is compared to an output voltage specification.
Other systems, methods, features, and advantages of the invention will be or will become apparent to one skilled in the art upon examination of the following FIGS. and detailed description. All such additional systems, methods, features, and advantages are intended to be included within this description, within the scope of the invention, and protected by the accompanying claims.